Provided that only about 10% of the observed UFDs appear to contain highly r-process enhanced stars (e.g. ), it seems evident that the responsible event is rare but individually prolific, such as NSMs. Thus assuming that such a merger is the most promising site for their r-process elements, the question arises whether it is possible for UFDs to have experienced such rare events within their short SFHs (\(<\) 1 Gyr). It is still unclear how often NSM events take place. Applying a maximum likelihood analysis to the observed dwarf spheroidal galaxies (dSphs) and UFDs,  have suggested that the expected NSM rate is \(5\times 10^{-4}-2\times 10^{-3}\)  per CCSN, which corresponds to a single NSM event per \(500-2000\)  CCSNe. Adopting a typical stellar initial mass function (IMF), about \(500-2000\)  CCSNe can be hosted in a galaxy with a stellar mass of \(M_{\ast }\approx 10^5{\,M_\odot }\)  (). Given that the stellar masses of Ret II and Tuc III are \(M_{\ast }=2.6\pm 0.2\times 10^3{\,M_\odot }\)  ([1]}) and \(M_{\ast }=0.8\pm 0.1\times 10^3{\,M_\odot }\)  (), respectively, such UFDs are less likely to host even a single NSM event during their SFHs.
